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• Stan79
• By Stan79 28th Nov 17, 7:01 PM
• 15Posts
• 0Thanks
Stan79
Hi all,

Does anyone have any experience working out the running cost of an Air Source Heat Pump?

I've been very bad at recording readings from it so only have a few readings plus the start date to calculate from... in principle though, is this equation right?

kW used / (Days elapsed x 24hours) x tariff price per kW = cost per day

So, last winter would be:
2682kW / (87 days x 24 hours) x £0.21 = £0.27 per day

And, this summer would be:
719kW / (192 days x 24 hours) x £0.21 = £0.03 per day

Does that look right? Many thanks in advance for any help!
Page 1
• Cardew
• By Cardew 28th Nov 17, 10:37 PM
• 27,360 Posts
• 13,390 Thanks
Cardew
If your ASHP used 2,682kWh in 87 days, that is an average of 30.83kWh a day and an average of 1.28kWh per hour over the whole 87 days. If you pay 21 pence for a kWh(extremely high cost) then it costs £6.47 a day and 27p an hour.
• matelodave
• 28th Nov 17, 10:59 PM
• 3,582 Posts
• 2,228 Thanks
matelodave
I think we need a bit more info. Are the consumption figures you are giving for the ASHP alone or for the whole house.

Is the ASHP on a seperate meter or have you got in on the day rate of an E7 tariff or some strange complex metering system. As Cardew says 21p a kwh is insanely high what tariff are you on. I'm moaning about having to pay 11.55p/kwh to run mine.

My ASHP cost very little to run in the summer but iit can look quite expensive in the winter but I reckon mine uses around 3000-3500kw a year which equates to between £350 and £400 a year.

As it responds to the house heating requirements and it has weather compensation it's consumption can vary between 10-50kwh in a day depending on how cold it is outside. That's anywhere between £1-£6

You can only determine what it's using by continuously monitoring it's consumption.
Last edited by matelodave; 28-11-2017 at 11:03 PM.
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• Stan79
• By Stan79 28th Nov 17, 11:01 PM
• 15 Posts
• 0 Thanks
Stan79
Hi there,

The 2682 figure is just a kW figure.... not a kWh figure!

Stan
• Stan79
• By Stan79 28th Nov 17, 11:06 PM
• 15 Posts
• 0 Thanks
Stan79
The figures given are for the heat pump only.
I'm on a Superdeal/Flexiplus setup where there are three tariff prices:
Day @ 20.77p / kWh
Night @ 10.99p / kWh
Stored heat @ 9.92p / kWh

Storage heaters heat the old part of the house and a new extension has a wet underfloor setup powered by the ASHP
Last edited by Stan79; 28-11-2017 at 11:08 PM.
• Stan79
• By Stan79 28th Nov 17, 11:11 PM
• 15 Posts
• 0 Thanks
Stan79
The usage figure i'm quoting is the kW used by the heat pump. Not kWh.
• matelodave
• 29th Nov 17, 9:00 AM
• 3,582 Posts
• 2,228 Thanks
matelodave
Energy consumed by the heatpump will be measured in kwh, ie if it uses 1kw and it's on for one hour then it's used 1kwh. Your leccy meter measures in kwh

Heat energy produced by the heatpump is also measured in kwh and is done by using a heat meter which measures the temperature of the water going into the heatpump, the temperature of the water leaving the heatpump and the volume of water flowing through the pump. These are integrated together which results in the quantity of heat produced by the pump.

The COP of the heatpump is ithe difference between the energy supplied to the heatpump from the electricity supply and the heat energy output from it. So if it consumes 1kwh of leccy and produces 3.2kwh of heat it has a COP of 3.2.

The quantity of energy produced by the heatpump varies with the outside temperature and the flow temperatures so isn't a constant.

Most heatpump COPs are spec'd at 7 degrees ambient to 35 degrees flow (7/35) and a change to either of those temperrtures will result in a different COP.

If you assume that your heatpump has a COP of 3 then your 2682kwh of leccy should have produced about 8000kwh of heat which means you are paying the equivalent of around 7p/kwh during the day and about 3,6p/kwh at night assuming you get some benefit from using it from the off-peak supply.

I'm interested in how you are measuring the consumption - is it separately metered on it's own circuit, indepenedant from everything else or have you got an energy monitor connected to it?
Last edited by matelodave; 29-11-2017 at 11:15 AM.
Love makes the world go round - beer make it go round even faster
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• Cardew
• By Cardew 29th Nov 17, 9:35 AM
• 27,360 Posts
• 13,390 Thanks
Cardew
Hi there,

The 2682 figure is just a kW figure.... not a kWh figure!

Stan
Originally posted by Stan79
Believe me the figure of 2,682 used over 87 days is kWh!

Your heat pump could be rated at anything between 9kW and 14kW

As said above, the price you are paying for electricity is unbelievably high. There are plenty of tariffs available where you pay around 12p/kWh to13pkWh all day and night i.e. 24/7, and that includes all the electricity consumed in the house - not just for the ASHP.
Last edited by Cardew; 29-11-2017 at 9:40 AM.
• Stan79
• By Stan79 29th Nov 17, 6:53 PM
• 15 Posts
• 0 Thanks
Stan79
Ah... i've found part of the problem... The meter i have been quoting is a meter linked to the RHI payments and measures the amount of hot water produced in kW. What a prat. Sorry to waste your time.

Still no closer to working out how much electricity the heat pump is consuming!!!

Changed tariff today and am now paying 16p day, 8.5p night, 7p stored/heat. Works out to £200 saving based on projection and cheaper than their lowest single rate tariff. Projected bill is £726 for a family of 4 in a 4 bed house.

As i say though, I'm still no closer to working out how much electricity the heat pump is consuming!!!

It's a 10kW model...
• matelodave
• 29th Nov 17, 7:32 PM
• 3,582 Posts
• 2,228 Thanks
matelodave
If you are having to provide meter readings to get RHI then you should have two meters, one is the heat meter which works out how much energy your unit is producing and you should also have a separate electricity meter to record how much electricity you are inputting. so your RHI should be based on the difference between the two
Love makes the world go round - beer make it go round even faster
Look after our planet - it's the only one with beer
• Stan79
• By Stan79 29th Nov 17, 11:02 PM
• 15 Posts
• 0 Thanks
Stan79
I don't have to provide meter readings. I think the fitters installed it "just in case"...

Unless the control box for the heat pump logs kWh usage? I will have to have a look!
• matelodave
• 30th Nov 17, 8:31 AM
• 3,582 Posts
• 2,228 Thanks
matelodave
Ttis is what I've got www.energyhive.com/dashboard/dave which allows me to monitor my energy consumption. You can monitor it on a PC, phone or tablet and download the data if you wish

There's a similar device made by Efergy (The Efergy Engage which seems to use similar software and the same servers) Maplins are flogging them off cheaply at the moment, if you can find any left in their stores. £20 for a hub and transmitter. https://www.maplin.co.uk/p/efergy-engage-hub-kit-n67nw

Mine is monitoring the whole house, but as I've had it for several years I've got a pretty good idea of how to read it so I know what's on and when and most of it is for the heating at this time of the year.

It's possible to get extra transmitters to monitor different circuits. The sensors clamp around the supply cables so there's no requirement to make connections to the mains supply/ Although if you wanted to monitor just one device, like your heatpump, you'd have to clamp it round the live conductor in the cable that feeds it.
Last edited by matelodave; 30-11-2017 at 8:40 AM.
Love makes the world go round - beer make it go round even faster
Look after our planet - it's the only one with beer
• Cardew
• By Cardew 30th Nov 17, 11:02 AM
• 27,360 Posts
• 13,390 Thanks
Cardew
If you are having to provide meter readings to get RHI then you should have two meters, one is the heat meter which works out how much energy your unit is producing and you should also have a separate electricity meter to record how much electricity you are inputting. so your RHI should be based on the difference between the two
Originally posted by matelodave
Hi,
I must admit to knowing little about the detail of RHI payments, but I cannot see how you can have a heat meter to measure energy the ASHP is producing.

Even if a meter could measure the energy produced, what is the relevance of the figures obtained? If you and I have identical houses and ASHPs yet I am wasteful and use twice as much 'energy' as yourself, would I get twice the RHI payments? If not what is the point of measuring the energy produced?

From: https://www.ofgem.gov.uk/system/files/docs/2017/10/essentialguideforapplicants_rpiia_4.1_october_2017 .pdf

Most people won!!!8217;t need to install meters to join the
Domestic RHI and will be paid based on the annual
heat demand figure listed on their EPC,
My 'back of a fag packet' understanding of the RHI system for ASHP was was that the heating/hot water demand of the house was assessed by EPC - say 15,000kWh - and the COP(SPF) was assessed by MCS - say 3.0 - and the RHI payments were based on those assessed figures.
Last edited by Cardew; 30-11-2017 at 11:06 AM.
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